1. Field of the Invention
This invention relates to the polymerization of hydroxyl-endblocked polydiorganosiloxane oligomer using quaternary ammonium carboxylate and carboxylic acid as catalyst, also the polymerization in the presence of reinforcing filler.
2. Description of the Prior Art
Silicone polymers of both high and low molecular weights have been combined with various types of filler to make thickened compounds and greases, as well as reinforced polymer mixtures used to produce silicone elastomers. The method used commercially has produced polymer of the molecular weight desired, then combined it with the appropriate thickening or reinforcing filler material.
In U.S. Pat. No. 2,906,734, issued Sept. 29, 1959, Clark discloses the use of quaternary ammonium salts of the formula RR.sub.3 'NOR" and benzoic or monocarboxylic acid as a catalyst for curing a polysiloxane resin. The polysiloxane resin is required to have at least 0.8 percent by weight silicon-bonded hydroxyl radical based on the weight of the siloxane.
In U.S. Pat. No. 3,160,601, issued Dec. 8, 1964, Hyde discloses the use of amine salts as catalysts for the condensation of silicon-bonded hydroxyl groups. Hyde uses a salt of a phosphoric acid or a salt of a carboxylic acid and ammonia or amines as catalysts. The salt must be compatible in the system. The salt must have at least 6 carbon atoms.
In U.S. Pat. No. 3,997,496, issued Dec. 14, 1976, Razzano discloses a process of reacting a mixture of silanol endstopped perfluoroalkyl-substituted organopolysiloxane of 3 to 5 units alone or with a second silanol endstopped diorganopolysiloxane having 3 to 5 units in the presence of a non-bond-rearranging catalyst and removing the water of condensation. Suitable catalysts include amines and amine salts such as benzyltrimethylammonium acetate. The resulting polymer, having a viscosity from 2000 cps to 200,000,000 cps, can be mixed with reinforcing filler.